To the long list of reasons that make abusing heroin so dangerous, add this: acetyl fentanyl.

According to a recently published study in the Annals of Emergency Medicine, acetyl fentanyl is a "quasi-legal" synthetic opiate often mixed with heroin sold on the street.

It's potent stuff — five to 15 times stronger than heroin — but users typically have no idea if it's in the dose they've just bought.

John Stogner, the study's author, said emergency workers should be prepared for a rise in overdoses tied to the use (unwitting or otherwise) of acetyl fentanyl. And they may find that "the standard dose of antidote (naloxone) doesn't work," he said in the study's introduction.

"Larger or additional doses are necessary when acetyl fentanyl is responsible. It's never good to lose time between overdose and treatment," Stogner, who is with the department of criminal justice and criminology at the University of North Carolina, Charlotte, said in the study.

"People who abuse heroin and prescription drugs need to remember that these things can be cut with anything, including acetyl fentanyl," Doreen Lockwood, the chemical dependence director at Putnam Family and Community Services, said. "People are unaware they're ingesting it."

Acetyl fentanyl can be used on its own, without being cut into heroin or other drugs, but Lockwood said she hasn't seen evidence of that happening here.

The drug's quasi-legal status makes it particularly troublesome for authorities and treatment providers. As Stogner explained, acetyl fentanyl is not cleared for human consumption. But if products containing it — like plant food or bath salts, mentioned as examples in the study — are labeled "not for human consumption," those products may be legal.

"Clever and well-informed drug distribution networks will likely take advantage of the legal loophole and profit by replacing or cutting a highly-regulated drug with this less regulated one," Stogner said in the study.

Officials in Putnam, Rockland and Westchester counties have requested help from the federal government in their efforts to combat heroin abuse.

"We have to remind people that treatment is available and recovery is possible," Lockwood said.